Stress determining device



22, 1942.. w. PABST E-rAl. 2,306,3j17

STRESS DETERMINING DEVICE Filed sept. 2s, 1958 s sheets-sheet 1 MAGNET/C muRA/o/v ARM/mmf wmf JWM @M WM w( @wml/f, l

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Dec. Z2, i942. w. PABST ETAL STRESS DETERMINING DEVICE Filed Sept. 23. 1938 3 Sheets-Sheet 2 Dec. 22, E942.

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sTREss DETERMINING DEVICE 5 SheeEs-Sheet 3 Filed Sept. 2:5, 1938 @MMM 50W/ l mf? AQw/mwaf,

Patented Dec. 19.42

STRESS DETERMINING DEVICE Wilhelm Pabst and Werner Knoll, Hamburg,

Germany; vested in the Alien Property Custo- Application September 23, 1938, Serial No. 231,436

1 Claim.

This invention relates to measuring instruments and has special reference to an apparatus and method for measuring such stresses as are due to effects of elongation, torsion, pressure, and kindred types of distortion.

More particularly, the invention relates to a measuring apparatus wherein the measurements are determined by comparison of the oscillations of tensioned vibrating wires, the vibration of one wire being controlled or governed by the stress to be measured.

One important object of the present invention is to provide a novel apparatus and method for the purpose set forth, wherein the two wires are kept constantly vibrating by actuating electromagnets arranged in independent oscillating circuits whereby ample time is provided for performing the manual operations incident to effecting the measurement.

A second important object of the invention is to provide means for optically comparing'the oscillations of the two wires.

With the above and other objects in view, the invention consists of the method and apparatus hereinafter fully described and particularly pointed out in the appended claims, the apparatus being disclosed in the accompanying drawings.

In the drawings, like characters of reference indicate like parts in the several views, and- Figurek l illustrates a general diagram of one form of the complete apparatus including a comparison device for the two circuits;

Figure 2 illustrates a diagram of a form of comparison device utilizing an electron ray;

Figure 3 illustrates a diagram of a modified form of the device shown in Figure 2;

Figure 4 illustrates a diagram of a second modification of the device shown in Figure 2;

Figure 5 illustrates a diagram showing a form of comparison device employing electro-magnetically controlled mirrors;

Figure 6 illustrates a view similar to Figure 1, but employing a stroboscopic comparison device.

In the forms of the invention shown in Figures l and 6, there is illustrated a wire l held under tension by the stress in the object whose distortion understress is to be measured. The action of the object under stress is illustrated by the arrows A. At 30 is a source of direct cur- Y rent here shown as a battery. At 4 is a four element tube having an anode 3| vand a filament 32, current being supplied to the latter from the battery 33.

Germany August 9, 1938 (Cl. l265-1) mary 34 by a conductor 35 and the other tenninal of the battery 30 is connected by a conductor 36 to one terminal of a transformer primary 3l. A conductor 38 connects the remaining terminal of the primary 3 to the anode 3l. The remaining terminal of the primary 3l is connected by a conductor 39 to the grid 40 of the tube B. Conductor means il connects the conductor 35 with l terial, that the wire constitutes an armature for- One terminal of the battery 30 is connected to one terminal of a transformer pri-'1 these magnets. A conductor @l connects theremaining terminal of the secondary t3 with one end of the winding of the magnet 2 and a con.

ductor 48 connects the remaining terminal of the secondary 35 with one end of the winding of the magnet 3. The remaining ends of the magnet windings are grounded as at t9.

The apparatus also includes a comparison wire of magnetic material, one end of which is anchored as at 5t. The other end oi' the wire t is connected to a tensioning screw 'i by the operation of which tension on the wire t, and consequently its normal period of vibration, may be regulated. Magnets 3 and 3 are so positioned that the wire S constitutes an armature for these magnets.V A circuit arrangement 5l exactly similar to that described in connection with the magnets 2 and 3 is associated'with the magnets 8 and 9, the arrangement having a four element tube t3, batteries 52 and 53, and transformers 5d and 55. Because of the identity of the two arrangements, the various conductive connections of the arrangement 5i are not deemednecessary here to be described.

in the form of the invention shown in Figure 1, there is disclosed a comparison device 5 having a pointer 56 which traverses a scale 51 in either direc tion from the central or zero point of the scale. A conductor 58 connects one side of the instrument 5 to the conductor dl of the test unit and a conductor 59 connects the other side of the instrument 5 to the conductor 60 ofthe standard unit.

By means of the circuits thus formed, the magnets2 and 3 and the magnets 8 and 9 will have oscillatory currents established in their windings which will cause vibrations in the Wires l and 6. It will be obvious to anyone skilled in the art that the current supplying these circuits is an alternating urrent. This is mentioned only because one knowing nothing of this art -turn, react upon the secondary circuits, thus causing the pointer 56 to move in one direction or the other unless the wires vibrate in unison, thus eliminating the heterodyning effect. If the pointer moves in this manner, tension on the comparison wire 6 is adjusted by rotating the screw 1 until the pointer rests at the zero point of the scale 51. In order to determine the tension on the wire 6, the screwv1 may be provided with a pointer 6I traversing a scale 62 which may be graduated to read in suitable stress units.

In the form of the comparison device shown in Figure 2, there is shown a cathode ray tube Il provided with conventional means for producing an electronic ray 6 I which imp inges upon a screen I4, This ray passes between two pairs of plates I2 and I3, the pair I3 being at right angles to the pair I2. vOne of the plates I2 is connected to the conductor 58 and the conductor 59 is connected to one of the plates I3. The remaining plates I2 and I3 are grounded as'at 62 and 63, respectively.

Similarly, in Figure 3 there is provided the tube II and screen I4 but in this form the plates are replaced by pairs of coils I6 and I1, one pair having its coils at right angles to the other pair so that the electronic ray 6I' passes between the coils of the respective pairs. The conductors 58 and 59 are each connected to one coil of a respective pair. Each pair of coils is connected in series and the pairs are groundedas at 64 and 65.

Figure 4 illustrates a. further modification employing a single pair of plates I8 and a single pair of coils I9 connected and grounded as be` fore.

In each of these forms, the oscillatory currents flowing through the conductors 58 and 59 cause the ray 6I to oscillate, thus producing Lissajou figures I on the screens I4. Whenever a hetero' dyning effect exists, the Lissajou figure produced will change in shape or in position, or in both shape and position. When, however, the wiresA I and 6 oscillate in unison or in orthodynic relation, the Lissajou figure will maintain constant shape and position.

In the form of the comparing device shown in Figure 5, there is provided a pair of minors 20 and 2l oscillating under the influence of magnetic means 66 and 61 receiving current from the conductors 58 and 59. Light rays 22 impinge upon these mirrors and are reflected to a screen 24 on which when the circuits are in orthodynic relation, they form a closed and stationary Lissajou figure'.

In the form shown in Figure 6, a housingv 25 is provided with an opening 26 through which the eye 21 of an observer may observe a point on the wire 6 which is in constant vibration. An incandescent lamp 28 emits light intermittently in conformity to the ilow of current through the conductor 58, the conductor 53 being omitted in this form. Under these conditions, the light ascuas? from the lamp 28, transmitted through a suitable lens arrangement, impinges upon a point upon the wire 6 which, due to the stroboscopic effect, appears to be stationary whenever the wires I and 6 are in orthodynic relation, since each flash of light from the lamp will strike the wire 6 when the latter is at a. definite position of oscillation,

i 30 indicates a battery which is used for starting the operation and corres onds to an anode battery (B battery), while th filament heating battery (A battery) is shown t 33. It is perfectly obvious that these two batteries will ynot continuously discharge their current into tube 4, but that a switch (not shown) is provided,

as usual, for the purpose of closing the circuit when the apparatus is to be set in motion. This switch is of` a conventional type. With regard to the mode of operation of the apparatus, which is actually in Ause for the purpose stated with special advantage in many cases and which. in the manner described, is easily understood, the following is to be noted: The switching in of the anode battery 30, with the aid of the above mentioned switch, will produce a sudden surge or impulse of voltage, as the potential in the anode circuit jumps from zero to the value of the anode voltage. The switching in of the anode battery is, therefore, like all switching performance, an alternating current operation as a result of the sudden change in potential. This means that this voltage impulse caused by said switching also occurs in the secondary winding of the output transformer to which it is inductively transmitted. The energization winding of the motor magnets 2 or 8, is, however, also in the circuit of the secondary winding of this output transmitter, i. e. the excitation magnet is energized for a short period by the voltage impulse occurring at the instant of the switching of the anode battery, and, as a result, the measuring string is also attracted for a short period.

'I'he movement made by the measuring `string .will react upon the second magnet 3 or 9 to produce an induction change, since the measuring string made of steel moves in the manner of an armature at the poles of said magnets 3 or 6, thus producing in their windings for a short period, by its movement an electromotive force (EMF), which will reach, through cable 48 or 60, the input transformer, and from there will pass inductively to the grid of the amplifier tubes 4 or I0, This input energy is amplified in the tubes and is fed back through the output transformer to the magnets 2 or 8.

This return coupling operation will cause the strings to gradually swing from their natural frequencies to a condition of mechanical vibration the amplitude of which, at flrst, increases continuously. After a certain period, however, a constant amplitude is obtained as a result" of the damping produced in the return coupling circuit.

'I'he above described operation from the initial vibration, the state 'of maintained vibration until constancy of amplitude is achievedjwhlch is performed in a fraction of a second, is referred to in the technical literature as mechanical-electric return coupling.

According to a different theory the operation nds its explanation in the fact that due to the sensitiveness of the apparatus the strings 6 and I are never in a complete position of rest, but are continuously performing` small vibrations, which will likewise function to produce the necessary state for the'measuring procedure, i. e.,

vibrations of the strings, which are then strengththe stress is to be measured, a second independently tensioned wire of magnetic material, manually controlled means for adjusting the tension of the second wire, a first oscillatory circuit for the rst wire` including electro-magnetic means for which the iirst wire forms an armature, a second oscillatory circuit for the second wire, havingsubst'antially the same construction and characteristics as the first oscillatory circuit, in-

cluding electro-magnetic meansfor which the second wire forms an armature, the electro-magnetic means serving to keep' the wires constantly in vibration, and means to compare the oscillations in said circuits, said wires each being free from the oscillatory field of the other.

WILHELM PABST. `WERNER KNOLL. 

